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describe the effect of using --memory-swap=0 (#2854) 

* describe the effect of using --memory-swap=0

Signed-off-by: Zhiguo Deng <bjzgdeng@linux.vnet.ibm.com>

* Edits

* Rewording about definition of swap

* Reworking for clarity of all the different ways it can be unset
This commit is contained in:
Joe Deng 2017-04-26 05:44:16 +08:00 committed by John Mulhausen
parent 90d0b00d78
commit 9745a627ea
1 changed files with 28 additions and 11 deletions
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39
engine/admin/resource_constraints.md
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@ -38,16 +38,33 @@ for [Memory Resource Controller](https://www.kernel.org/doc/Documentation/cgroup
### `--memory-swap` details
- If unset, and `--memory` is set, the container can use twice as much swap
as the `--memory` setting, if the host container has swap memory configured.
For instance, if `--memory="300m"` and `--memory-swap` is not set, the
container can use 300m of memory and 600m of swap.
- If set to a positive integer, and if both `--memory` and `--memory-swap`
are set, `--memory-swap` represents the total amount of memory and swap
that can be used, and `--memory` controls the amount used by non-swap
memory. So if `--memory="300m"` and `--memory-swap="1g"`, the container
can use 300m of memory and 700m (1g - 300m) swap.
- If set to `-1` (the default), the container is allowed to use unlimited swap memory.
`--memory-swap` is a modifier flag that only has meaning if `--memory` is also
set. Using swap allows the container to write excess memory requirements to disk
when the container has exhausted all the RAM that is available to it. There is a
performance penalty for applications that swap memory to disk often.
Its setting can have complicated effects:
- If `--memory-swap` is set to a positive integer, then both `--memory` and
`--memory-swap` must be set. `--memory-swap` represents the total amount of
memory and swap that can be used, and `--memory` controls the amount used by
non-swap memory. So if `--memory="300m"` and `--memory-swap="1g"`, the
container can use 300m of memory and 700m (`1g - 300m`) swap.
- If `--memory-swap` is set to `0`, the setting is ignored, and the value is
treated as unset.
- If `--memory-swap` is set to the same value as `--memory`, and `--memory` is
set to a positive integer, the effect is the same as setting `--memory-swap`
to `0` (the value is treated as unset).
- If `--memory-swap` is unset, and `--memory` is set, the container can use
twice as much swap as the `--memory` setting, if the host container has swap
memory configured. For instance, if `--memory="300m"` and `--memory-swap` is
not set, the container can use 300m of memory and 600m of swap.
- If `--memory-swap` is explicitly set to `-1`, the container is allowed to use
unlimited swap, up to the amount available on the host system.
### `--memory-swappiness` details
@ -97,7 +114,7 @@ and higher, you can also configure the
The CFS is the Linux kernel CPU scheduler for normal Linux processes. Several
runtime flags allow you to configure the amount of access to CPU resources your
container has. When you use these settings, Docker modifies the settings for
container has. When you use these settings, Docker modifies the settings for
the container's cgroup on the host machine.
| Option | Description |